Various methods have been suggested for remote sensing of the path-averaged wind. Most of them depend on temporal analysis of reflected laser beam intensity fluctuations that are produced when refractive-index eddies are drifted by a wind across the laser beam.
R. S. Lawrence et al, in Applied Optics, Vol. 11, No. 2, pp. 239-243, describes the use of laser scintillation patterns to measure path-averaged wind velocity by measuring a time-lagged covariance function with spaced detectors.
Ting-I Wang et al, in Applied Optics, Vol. 20, No. 23, pp. 4073-4081, compares various methods with regard to their immunity to the turbulence strength changes and arrives at the conclusion that no method is ideal, mainly due to turbulence spectrum changes.
L. C. Andrews et al, in J. Opt. Soc. Am, Vol. 16, No. 6, pp. 1417-1429, whose disclosure is incorporated herein by reference, in their heuristic model of optical scintillation, shows the existence of a definite form of correlation between the turbulence strength and the turbulence spectrum. In accordance with this model the turbulence spectrum is characterized by a two-scale behavior: large scale for refractive irradiance fluctuations and small scale for diffractive irradiance fluctuations. The strong turbulence and the weak turbulence states are characterized mainly by large scales whose “life time” is significantly longer than the “life time” of the small scales, which exist mainly in the middle turbulence case.
The turbulent eddies shift with a wind, so their center moves in the wind velocity. These eddies cross a laser beam (or field of view of a receiver) and the temporal turbulence spectrum of reflected laser beam fluctuations, on which measurement most of the methods mentioned above are based, depends on turbulent eddy sizes, on a laser beam cross diameter (or field of view of a receiver) and on the “life time” of the turbulent eddies. Measurements that do not consider correlations between an atmosphere turbulence strength and spatial-temporal spectrum behavior become unpredictable.
U.S. Pat. Nos. 4,182,570 and 6,247,259, and PCT Published Patent Application WO2005/050254 describe various methods and devices for measuring wind speed normal to the path from the generated signal. It is stated in the patents that the methods and the devices based on cross-covariance function analysis can be applied for meteorological determinations and to fire control systems. It is mentioned that unpredictable changes in a spatial-temporal spectrum of atmosphere turbulence impact on the mathematical analysis results, but any methods for carrying into practice a correlation between an atmosphere turbulence strength and spatial-temporal spectrum of atmosphere turbulence are not described.